I can’t speak of the AMEX Platinum as it relates to your question as I do not have the card. If you get the AMEX Aspire, you will be given Hilton Diamond status and will earn 34 Hilton points per dollar spent at Hilton properties BEFORE factoring in current promotions. (This assumes you select points and points as your earning preference. You get 10 base points per dollar, plus another 10 diamond bonus points per dollar, plus 14 points per dollar paying with the AMEX Aspire card, yielding 34 points per dollar BEFORE factoring in promotions). With the upcoming double points promo, you will earn 44 points per dollar after your first stay. (10 base points, 10 double base points, 10 diamond bonus points, plus 14 points for AMEX Aspire, yielding 44 points per dollar)

If you value Hilton points at $0.005 per point (ie one half cent per point), you effectively earn a 22% bonus (or rebate) on all Hilton stays paid for with an AMEX Aspire card under the upcoming promo (after the first stay). Only you can tell if that is an acceptable rate of return relative to what you are currently receiving with Marriott. Good luck with whatever you decide, and happy points hunting!